Epoxy compositions and their curing techniques are well-known and the patents issued on curable epoxy compositions number in the hundreds. Known curing agents include, among many others, polycarboxylic acids and anhydrides, amines, polyamides, imidazoles, and the like. Representative curing agents are described in U.S. Pat. No. 3,336,241. These curing agents may be employed with one or more catalysts or accelerators such as the stannous salts of monocarboxylic acids.
It will be appreciated that each and every one of the known epoxy-curing systems exhibits advantages over other systems, and, as importantly, disadvantages over the same systems. There is, of course, a continuing need to develop better epoxy curing compositions.
An epoxy system which is not only simple and produces rapid curing, but also produces cured epoxy compositions exhibiting excellent physical properties has been developed. This curable composition comprising (1) an epoxy resin and (2) a curing amount of at least one "hard cation" catalyst is described and claimed in copending patent application Ser. No. 330,412, filed Dec. 14, 1981.
There is a continuing need and desire to modify curable systems in order to maximize physical and/or chemical properties as well as to produce more economical formulations. Accordingly, it has now been found that a portion of the epoxy in the composition of Ser. No. 330,412 can be replaced with one or more compatible comonomers, preferably an ethylenically unsaturated monomer, and more preferably, styrene, without significant reduction in physical properties.